Magnetic data store



Aug 2 1966 R. l.. GRAY, JR 3,264,62

MAGNETIC DATA STORE Original Filed Deo. 24, 1958 PERMISSIVE AND CLEARINGPULSE SOURCE READ RESTORE CURRENT SOURCE DATA SOURCE DATA UTILIZATIONDEVICE CONTROL STGNAL SOURCE AGENT United States Patent O1 hee 3,264,621Patented August 2, 1966 Michigan Continuation of application Ser. No.782,914, Dec. 24, 1958. This application Mar. 25, 1963, Ser. No. 269,833

12 Claims. (Cl. 340-174) The present application is a continuation ofSerial No. 782,914, led December 24, 1958, and now abandoned.

It is well known in the art of electrical data processing andcomputation to store information in magnetic materials of highretentivity by coding such information in binary form and arbitrarilyassigning to the two possible directions of retentivity of a magneticelement a correspondence with the two possible values of a binaryelement of information. It is almost universally desired thatinformation so stored be recoverable in the form of an electricalsignal. Two principal techniques have been found technically andeconomically feasible to do this. In one case (as in tape, drum `anddisk stores) the magnetic material is moved rapidly past a sensing orreading head in whose windings voltages are induced which arerepresentat-ive of the state of magnetization of the magnetic material.Such a method is not ordinarily destructive of the information thusstored, but it has the disadvantage of requiring rather high-speedmotion within close mechanical tolerance, and a certain access time mustordinarily be allowed for the desired information to become accessibleto the head. Fixed or mechanically static stores employing large numbers-of magnetic elements are commonly used where it is not possible topredict which particular item of information will be required at a giventime, and random access is therefore highly desirable. However, thecommon way of converting such stored magnetic data into an electricalsignal is conventionally that of applying to the magnetic element afield which will drive the element to saturation in the direction of theeld; if the element was yremanent in the opposite direction, the largeflux change involved in its reversal will induce a voltage in conductorscoupled to the magnetic element. This mode of reading out theinformation thus stored always leaves the element magnetized in thedirection of the reading field, and thus destroys the storedinformation. There are many operations where the same information isrequired again and again and, to employ a store with destructiveread-out in such a connection, it is necessary to perform what is knownas regeneration, which is quite simply the external storage andsubsequent recording of the information just read out. This requirestime and equipment, and is therefore not desirable; however, it is atolerable evil in view of the great advantage of random access and highoperating speed obtainable by the use of mechanically static stores. Itis actually common practice to provide complete computing systems withvarious kinds of magnetic stores, which fact is perhaps the bestpossible evidence that no particular type of conventional data store isinfinitely superior to any other.

Until recently, it has been conventional to employ separate pieces ofmagnetic material, usually closed cores, to store in static storesindividual items of binary information, or bits. However, the use ofextended pieces of magnetic material having a capacity for a number ofbits in a single such piece is known (e. g., Bobeck, Bell SystemTechnical Journal, November 1957, pp. 13194340). In general, theboundary lines between the different portions of such a piece ofmagnetic material which are employed to store dilferent bits ofinformation are determined by the magnetic fields which are externallykapplied to the magnetic material. lt has been recognized that it isnecessary to allow sufficient space between adjacent portionscorresponding to different bits so that the magnetic fields applied toaifect only one such portion will not affect an adjacent portion. Thereading methods which have thus far actually been made known to thepublic all involve destruction of the stored information.

My invention teaches a use of-a single piece of magnetic material tostore multiple bits of information, with nondestructive readout,although the value of any stored bit may be changed at will. All theadvantages of random access, compactness, high speed of operation, andother desirable features of mechanically static stores are retained.

Thus an object of my invention is to teach a method of non-destructiveobservation -of stored data in a mechanically static magneticinformation store.

Another object of my invention is to provide an inexpensive, compactdata store of large capacity in which the reading operation isindependent of the operation of writing.

Other objects and advantages of my invention will become apparent in thecourse of the following description and specication of my invention.

To facilitate the explanation of my invention, I provide drawingsattached hereto, as follows:

FIGURE. l represents a data storage device for storing fourbinary-valued bits of information, and reading the stored informationnon-destructively, in accordance with my invention.

FIGURES 2a, 2b and 2c representa development of a portion of themagnetic material represented in FIGURE 1, with an indication of appliedmagnetizing elds and resulting senses of magnetization, for the betterexplanation of the principles of operation of my invention.

in FIGURE 1, 21a and 2lb are central conductors around which arewrapped, respectively, strips of magnetic material 22a and 22h, having apreferred direction of magnetization substantially along their length,'and showing a substantially rectangular hysteresis loop or curve ofmagnetic ux density versus magnetizing field. Such material is known inthe present art and may be, for example, unannealed 4-79 molybdenumpermalloy (nominally 4% Mo, 79 Ni, 17% Fe), which has not been annealedafter its last rolling. A suitable size of such material is a strip oneeight-thousandth of an inch thick and seventeen onethousandth yinchwide. The direction of wrapping is such that the length of the strips22a and 22b is helical about the axis of the respective centralconductors 21a and 2lb, and thus the direction of easy or preferredmagnetization is also helical labout such central axes. This form ofconstruction facilitates the explanation of my in- Vention; it isdescribed in co-pending application, Serial No. 748,405, tiled July 14,1958, and now abandoned, entitled Helical Wrap Memory;7 of John D.Blades, which is assigned to the assignee of this application. At twodifferent longitudinal locations along the wrapped assemblies of 21a and22a and of 2lb and ZZb, there are wound solenoids 23a and 2317. Alsoaround the assemblies of conductor 21a and tape 22a, and of conductor2lb and tape 221), and substantially intermediate the ends of thewinding of solenoid 23a, there is wound solenoid 24a, which may beoutside or inside of solenoid 23a, or interwound with it. It is basic tomy invention that solenoid 23a shall produce a magnetizing eld uniformin sense over a portion of tapes 22a and 22h greater than and includingthat part of tapes 22a and 22b over which solenoid 2da produces aconsiderable magnetizing field. In other words, solenoid 23a whencarrying current produces a substantial magnetizing eld over a portionof tapes 22a and 22b, and solenoid 24a when carrying current produces asubstantial magnetizing eld over only a part of such portion. The knownart teaches a number of various 22a, presenting it as fiat according todraughtingconven-y tions. This representation has'the convenientproperty that the axis or direction of easy magnetization appears as astraight line, so that direction or sense of magnetization also appearsas a direction along such line. FIGURE i 2a represents the statedportion of tape 22a with all parts of that portion magnetized in thesame direction, as indicated by the arrows lola, 102g, and 103m Thiswould be the effect of applying by solenoid 23a a magnetizing fieldcomponent directed to the right and exceeding the coercive force `of thematerial of 22a. FIGURE 2b represents a situation identical with that ofFIGURE 2a except that` the direction `of magnetization of theintermediate part of the represented portion of tape 22a, generallyindicated by arrow 102b`, is opposite in direction from that representedin FIGURE 2a by arrow 102:1. This effect would be produced by theapplication by passage of current through solenoid 24a of a magnetizingfield opposite in direction, or sense, to that applied by solenoid 23ato produce the situation represented in FIGURE 2a. In thesituation'represented in FIGURE 2a there is a substantially continuousmagnetic ux along the entire length of the portion of 22a, existingprimarily within the tape 22a, and with practically no magnetic uxleaving tape 22a at the boundaries between 10151 and 102e, or between10211 and 103e. 2b, on the other hand, requires the existence ofmagnetic poles `at the boundaries between arrows lla and 102b, andbetween'arrows 102b and 103e. An alternate way of expressing thisphysical fact is `to saythat magnetic flux, representedby arrows 105,leaves the tape `22a at therboundary .between arrows 101e and 192]) andreturns at the boundary between arrows 102]) and 103a. This situation,by well known physical principles, leaves the central part of theportion of strip 22a, where arrow 10211 is shown, subjected to amagnetizing field which tends, butfmay be dnsutiicient in amplitude, toreverse the magnetization of the central part to that sense or directionrepresented by arrow 102a. If there be applied by passage of currentthrough solenoid 24a a magnetizingy field component in the directionrepresented by arrow 104, a certain amplitude of that field component inthe presence of the assisting fields represented by arrows 10161 and103a, will suffice to reverse the magnetization of the central part,restoring the condition representedby FIGURE-2a. If, on the other hand,the condition of the represented portion of tape 22a is as indicated inFIGURE 2c, with all parts of the tape portion magnetized in the samesense, indicated by arrows 101i), ltl2b,'and 1Mb, the same amplitude ofmagnetizing field component represented by arrow 104 will not suiice toreverse the magnetization of the central part of the portion of tape22a, because the fields represented by arrows 1Mb and 103b will opposesuch reversal. It is true that the situations represented by FIG- URES2a and 2c, in which all parts of the portion of tape 22a are magnetizedin the same direction,.will result in` the existence of some magneticflux from the extreme ends of the tape portion returning throughthevspace external to the tape 22a; but, because the extreme ends of therepresented portion of tape 22a are -relatively distant from the ends ofthe central part where arrow 102 is drawn, the magnetizing field soproduced at the central part will be negligibly weak. It is a well knownfact that the demagnetizing effect of the poles of a bar magnet upon thecenter of such a magnet `becomes less and less as the .bar magnet ismade longer and longer; and a parallel situation exists here.

Given the preceding explanation of the physical phenomena underconsideration, the mode of operation of The situation represented inFIGUREr 4 1 my invention may be somewhat `more vspecifically described.The `entire portioncf tapeZZa represented in FIGURES 2a, 2b, and 2cwillbe used to store a given item of binary information, byappropriately magnetizing such portion by passing appropriate, currentthrough solenoid 23a. Employing, for simplicity, the terrns-oner-V andzero to denote the two possible valuesof an element of information, ythesituation represented `by FIGURE 2a will be described as the one stateof thetape portion, and that represented by FIGURE 2c will vbe describedas the zerof state Iof the tape portion. These both represent statescorresponding to recorded information. .T o determine what informationis thus recorde'cLa readingr field component inthe sense of arrow lb(FIGURESV 2b,

2c) is applied by passage of current through solenoid 24a.

The' magnitude of this field component is suicient so that, if the tapeportion was in the -one condition (FIGURE 2a), the central part of thetape portion will be reversed in magnetization, passing to the staterepresented in 'FIG- URE 2b'. A substantial change in the'flux throughthe central part of the` tape portion-,Will occur, inducing a voltage inany conductor `linked with the central part. If, on the other hand, theVtape portion was inthe zero condition, the application of the readingfield will'produce only a negligible effect on the magnetization of thetape portion, simply driving the central part through the very slightflux change from remanence to saturation, and inducing only a veryIsmall voltage in any conductors linked therewith. Thus the condition ofthe tape portion,l if inthe zero state before reading, wil-l beessentially unchangedl after reading; FIGURE 2c represents either ofthese states.

The reading operation described has not destroyed the storedinformation, because the state of the .tape portion, afterrreading, isdifferent depending vupon whether a oneHor a zer0'was stored in itbefore reading. However, for a stored one thek reading operation does,

at least temporarily, alter the magnetic state of .the tapey Y portion,as represented bythe differences between FIG- URES 2a and2b. If lthecoercive force ofA the tape 22a is sufiiciently low, therestoringmagnetizingyeld pro vided by the extreme parts -ofl thertapeportion,l which remain -in the fone condition, may suffice to restoreythe central part of the tapeportionzto itsori-ginal or one state ofmagnetization immediately upon the `cessation of the reading fieldcomponent. However, it is possible to practice my invention evenwithmaterials having coercive forces so hghfvthat this :spontaneousrestoration does; not occur. A y'uniform restoration or regeneration fprocedure, `which may be applied without any knowledge;l ofy theinformation stored, will restorethe tape -to itstl pre-readingcondition.; This restoration procedure consists simply'in the.Vapplication, vbypassagejr of current through solenoid 24a, of, a fieldcomponent opposite inpdirection or sense to the reading field component,

and smaller in magnitude, so that, as described in they i precedingdiscussion of FIGURES 2b and 2c, it will v suffice to restore `the tapeportion yfrom thecozndition representedby FIGURE 2b` to the conditionrepresented i by FIGURE 2a, but'will not Ialter the `tape portion fromthe condition represented by FIGURE v2c.` It is tapparent that,logically, this restorationoperation may be performedV at any time.between lsuccessive ,reading operations.

jacent tape portions, all parts `of any given tape portion be leftmagnetized in the same direction, so that there Y will not :be ademagnetizing effect of opposing magnetization of different parts whichmayrender the Vstored sigt t nal less stable. Indeed, fthere -is noactual necessity for regarding the Arestoration field as anything but aspecified However, if lextreme density of recorded in-y formation is tobe achieved. =it is desirable that, to avoid f yaccidental and undesiredeffects lof operationsupon aderation of the device, but is overcome byt-he reading field component during the reading operation. Such acontinuing eld may be provided either by .passing a continuous currentof controlled magnitude through an additional solenoid wound togetherwith the reading solenoid 24a, .or by providing a continuous currentwhich flows through solenoid 24a but is .overcome by the application ofthe reading pulse current through solenoid 24a. From any point of view,the reading operation as described is non-destructive, in that there is.no necessity rfor perform-ing after reading an .operation dependentupon the particular values of information read out.

Considering FIGURE 1 once more, the following dimensions are given aspreferred for operation at moderately high speeds, of the order of oneand one-half microseconds for the reading and restoring operation. Itwill be recognized that oper-ation at lower speeds will render the useof somewhat increased dimensions permissible; while, for higher speedoperation, dimensions proportionately reduced so far as is feasible willbe preferable. The central conductors 21a, 2lb are of copper Wire #35A.W.G., corresponding to a nominal diameter of 5.614 mils, orthousandths of an inch. The tapes 22a, 22b are one eighth of .a milthick and 17 mils wide and are wound with no overlap or with overlap upto two-thirds of the tape width. Solenoids 23a and 23b are wound offorty turns of wire #29 A.W.G., corresponding to a nominal diameter of.11.-26 mils, to a total winding length of about 0.5 inch. Solenoids 24aand 24b are of ten turns of wire #36 A.W.G., corresponding to a nominaldiameter of 5.0 mils, to a total winding length of approximately 1/2inch; these solenoids are wound under solenoids 23a and 23hrespectively, and substantially centered under their respectivesolenoids. The wires are insulated with a conventional insulatingenamel, such as the product known commercially as Formvarf Spacingbetween adjacent ends of solenoids 23a and 23b is one tenth of an inch.

In order to illustrate the principles of my invention in an embodimentof moderate complexity, such as may be desirable -in modern computingand data-processing usage, I have represented 4in FIGURE l anarrangement of the various solenoids in such fashion as to permit theuse of certain means for selection of specific tape portions forrecording of data by the combined applications of various magnetizingeld components. As is described in more detail in the referencedapplication of Blades, it is possible to produce a resultant magnetizingeld substantially along the thelically disposed direction of easymagnetization of the tape 22a by producing a magnetizing field componentby passage of current through a solenoid, such as 23a, which componentwill be substantially along the central axis of conductor 21a or 2lb,.and by producing simultaneously a magnetizing field component circulararound conductor 21a by passing current through conductor 21a. Thus, inFIG- URE l, a conventional current flowing from lground thro-ughsolenoid 23al and out through its ungrounded end will produce at theleft-hand portions of tapes 22a and 22h a magnetizing field directedtoward the right .of the figure. If the current through the solenoid ismade of proper magnitude, this magnetizing field component will beinsufficient by itself to magnetize talpe 22a or tape 22b. If, however,a conventional current is fed from ground through conductor 21a and outthrough the ungrounded left end .of conductor 21a, this current willproduce a magnetizing eld component circular around conductor 21a. Byproperly controlling the magnitude of this current through the conductor21a, the magnetizing field component it produces may be made such thatit will combine With the magnetizing field component from solenoid 23ato magnetize from the zero to the one sense or direction that portion oftape 22a lying substantially within solenoid 23a. The magnetizing fieldcomponent produced by solenoid 23a will not suffice alone to magnetizeany portion of tape 22h; and the magnetizing field component produced bythe current through conductor 21a will not sufce -alone to magnetize theportion of tape 22a lying outside of solenoid 23a, particularly thatportion of tape 22a lying substantially within solenoid 23h. Thus it is.possible to apply permissive current through solenoid 2311 to render itpossible for currents through conductors 21a and 2lb to magnetize totheone state those portions of tapes 22a and 2211, respectively, which liewithin the effective eld produced by solenoid 23a. Individual bit orbinary one digit signals may be applied to conductors 21a and 2lb; and,as the preceding discuss-ion indicates, the presence or absence ofpermissive currents in solenoids 23a or 23h will determine the recordingor non-recording, respectively, of ones in the portions of tapes 22a and22h affected by the fields of the respective solenoids. The assemblyrepresented by FIGURE l may be regarded as consisting of two words (inconventional computer terminology) of two binary digits each. It is nowapparent that conventional reading current passed through solenoid 24ato ground will read out the data stored in the left-hand portions oftapes 22a and ZZb, the signals appearing inter alia .as induced voltagesat the terminals of conductors Zla and 2lb; and that reading currentapplied to solenoid 24h will read out the data stored in the right-handportions of tapes .22a and 2217, the signals .appearing again as inducedvoltages at the terminals of conductors 21a and 2lb. Likewise, it isapparent that a current in solenoid 23a opposite in direction to andsufficiently `greater in magnitude than the permissive current willreverse to the zero state the left-hand portions of .tapes 22a and 22b,FIGURE l, thus performing the function known in computer terminology asclearing the word stored in those tape portions.

Modern data-processing equipment is capable of extremely high operatingspeeds, at a considerable cost in equipment. Frequently economy requiresthat given pieces of apparatus be caused to perform a variety ofdifferent functions at different times, these functions either being sochosen that the same apparatus performs functions which logically.cannot be required simultaneously, or controls being provided so thatthe performance of one function is held in abeyance until a conflictingfunction has been completed. Since such divisi-on `of functions is verymuch an ad hoc property of a particular computer design, and since myinvention in this and other embodiments is applicable to a wide varietyof equipment requiring data storage, I have represented by rectangularblocks equipment whose functional capabilities will be defined anddescribed, and whose construction is taught abundantly by the known art;but .it must be understood that in an actual computer the elementsemployed to perform such functions might be employed to perform otherfunctions as well, and that the .apparatus performing the functionsassigned to a particular rectangular block might not appear in anact-ual computer or data-processing device as a single entity, bu-tmight be dispersed throughout the machine. This is as thou-gh, indescribing a novel alternator construction, I should represent aseparately driven exciter, although actual commercial construction wouldprobably incorporate the exciter shaft as part of the shaft of thealternator, both machines being driven by the same prime mover. Theteaching of my invention is claried by the use of such functionalblocks.

Control signal source lill is a source of control signals which areproduced at proper times, in accordance with the logical needs of thecomputing or data-processing system, to effect the results to bedescribed hereinafter. Data source 192 is a source of binary data to berecorded; in compliance with signals received over line 202 .fromcontrol signal source 101, it feeds appropriate electrical signals toconductor 31a and conductor Slb;

it has the characteristic that when not so functioning it presents arelatively high shunting impedance between conductors 31aand ground, and3i1b and ground, in order that Iit will not shunt out any large fractionof the currents flow-ing as a result of voltages induced in conductorsY21a and 2lb by the reading process. Permissive and clearing pulseVsource 103, in response to control signals received via line 203 fromcontrol signal source 101, will provide permissive current of a givenpolarity and magnitude or clearing current of opposite polarity andgreater magnitude to either solenoid 23a or 23b via conductors 33a or33b, respectively, accordingk to the particular control signal'received;it is apparent that, since there are yat least four possible functions4involved, these control signals may be coded pulses transmitted over asingle line, or line 203 may actually be replaced by several separateconductors to carry separately a signal to perform a given function, orany other combination of lines and signals known to the art may beemployed. Data utilization device 104 repre` sents Whatever physicalapparatus the construction and logic of the particular system mayyprovide to receive the stored data when it is read out from the storein the form of electrical signals. It is connected with control signalsource 101 byline 204 in order that it may be made to functionappropriately when control signal source 101, by activating otherassociated apparatus, causes .the reading of stored da'ta, and in orderthat` it may be rendered inactive or insensitive to the relativelylarger voltages applied to conductors 31a and 31b during the datawriting operation and to any voltages lgen-- erated during a clearingoperation. Read-restore current source 105,upon receipt of theappropriate control signals via line 205 from control signal source'101,applies to either` solenoid 24a via conductor 34a orto solenoid 241;via` conductor 34b'a reading current pulse of .given polarity andmagnitude; and (either immediately after the cessation of the readingcurrent pulse or, if desired, at'some time thereafter) a restoringcurrent pulse of opposite polarity from the reading current pulse, andof smaller magnitude. As is evident from the discussion of FIGURE 2, thereading pulse must be of ysufficient magnitude to reverse the sense ofmagnetization of the central part of a given tape portion despite theopposing magnetizing field provided by the end parts of the tapeportion; but the restoring pulse must be of such lesser magnitude thatit will restore the original sense of magnetization of the central partof the given tape portion if, but only if, itis assisted by themagnetizing field provided by the end parts of the tape portion.

A typical operating cycle of the device represented in FIGURE 1 :is thefollowing. Control signal source 101 via line 203 causes permissive andclearing pulse source 103 to send a clearing pulse of conventionalcurrent via conductor 33a through solenoid 23a to ground, whence itreturns to its source `103. Conourrently or sequentially permissive andclearing pulse source 103 sends a clearing n pulse of conventionalVcurrent via conductor 3317 through solenoid 23b to ground, whence itlreturns to its source 103.y Each of these clearing current pulses, inflowing through its appropriate solenoid, produces a magnetizing fielddirected to the left of the figure, `and of such magnitudeY that itscomponent along the direction of easy magnetization of the portions oftapes 22a and 22h lying within the solenoid exceeds the coercive forceof the tapes 22a and 22h. This will cause the four tape portions lyingwithin solenoids 23a and 23b to be magnetized in a direction having acomponent to the left of FIGURE 1. For purposes `of description, thisdirection is arbitrarily `assigned a zero significance, consistent withprevious description. Thus the entire magnetic store contains zeros oris said to be clearedf At some later time, controlisignal source 101sends a signal via line 203 to permissive and clearing pulse source 103which causes it to draw from ground through solenoid 23a via conductor33a a permissive pulse of conventional current of such smaller magnitudethan` the clearing pulse that the resultant magnetizingeldvvproduced bythe permissive pulse around .those portionsr of tapes 22a and 22b lyingsubstantially within solenoid 23o will have a component alongthedirection of easy rnag-A netization of` those ,tape portions Whichvisless than the coercive force .of the tape. Approximately` simultaneously,control signal, source 101 sends a signal via line y202` i to datasource 1021 which causes it to draw from ground through conductors 21aland 2lb via conductors 31a and 31h writing pulses ofconventionalcurrent corresponding to the fones bits `off-datal which areto be ,recorded or f Let it vbe-assuined that the data the tapeportionsl within the solenoids,` the., zero state of tape 22'b willcontinue.

An alternative to applying no currenty to conductor 2lb,

ias above described, is to modifythe characteristics of data source 102so thatit applies one signals by draw.

ing current from ground through the lappropriate conductor as abovedescribed,:but it also feeds currentto ground through the conductorswhere zero ris to be ret- 'corded to insure that there will be a slightmagnetizing eld'tending to preserve the zero state from destructionWherever it'already exists in the tape 22h. This alternative has thekadvantage that itis a positively applicable measure which reducessomewhat the stringencywith which the permissive pulse must beheldwithin its mail-V imum value; Le., it reduces some ofthe vdesigntolerances of the overall system. The .current which isremployed toinsure .the preservation of the zerostate must itself, of

course, be maintained sufficiently small {so that there is n o vdangerthat it will return to the zero state any portions of tape which-already(and properly) are in' the one state of magnetization. In actualpractice, the choiceof this alternative method will depend upon therelative cost and ease of controllingtolerances, and other variouskfactors. As "is indicated in' anumber pf the appended claims, it isprimarily the application of the proper maghi tudes of'magnetizingfields to the-specified parts ofthe tape upon which the operation oftmyinvention isbaSed,

and there are many Ways taught by the art existing priorY to myVinvention for iaccomplishing this. However, conl sistently with therequirement to store a one inthe left-- hand portion of tape 22a, therewill be drawn from ground through :conductor 21a via conductorla to datasource` 102, a Writing current pulse of such'magnitude that it willprodu'ce around conductor 21u 'a circularV mag- -nettizing field whichwill combine with the field of solenoid- 23a to produce a resultanthaving acomponent along the direction of easy magnetization of theleft-handportion `of tape 22a greater than the coercive tforce `ofthetape and in ksuch direction as to magnetizethat portion of tape v22a inthe one direction. Thezmagnitude of the Writing current drawn throughconductor 21a is limited so that.v

the magnetizing field produced hyit 'atf other portions of the tape 22a,particular-ly that p'ortionylying within sole'- noid25b, will have acornponentvalongetheV directionpf :easymagnetization of tape 22zz` ofmagnitude less than the .coercive force ofthe tape; thus thei'portion'oftape 22a lying Within solenoid 23ib' Will remain initscleared or zerost-ate.- Thus there is selectively recorded` in the left-hand portions,of theV `tapes 22a and 22b the wor .composed 'of-the binary digits, 1,'0. It is now obvious what modifications of the foregoing. describedprocedure will cause recording yof signa-ls in the-other portions of thetapes, and also that the number of solenoids along'a givenY tape :andconductor assemblyy may be vastly increased to provide greater datastorage capacity, and that the .num-t ber of tape and conductor'assemblies within the solenoids may be increased-to permit thesimultaneous storage or reading of a larger number of binary digits; andthe known art (to which partial general reference is made at the end ofthis specification) teaches many other modifications of the foregoing.

Given now that the desired data have been recorded in the data storerepresented in FIGURE l, let it be assumed that it is desired to readout the data stored in the lefthand portions of tapes 22a and 22]).Control signal source 101 via line 204 sends to data utilization device104 `a signal which causes data utilization device 104 to becomeresponsive to voltages appearing on conductors 31a and 31b. Controlsignal source 101 also sends via line 205 to read-restore current source105 a control signal which causes it to send through conductor 34a andsolenoid 24a to ground, whence it returns to its source, a pulse ofconventional current of sufficient amplitude to produce at the centralparts of the left-hand portions of tapes 22a and 2211 a magnetizingfield, oriented toward the left of the figure, whose component lalongthe direction of easy magnetization of the central parts of the two tapeportions will exceed the coercive force of the tape material. Then,*assuming that tape 22a within solenoid 23a -is remanent in the onesense or direction and that tape 22h within solenoid 23a is remanent inthe zero sense or direction, the central part of that portion of tape22a will be reversed in direction of magnetization, passing fromremanent flux density in the one direction (which is very nearly asgreat as saturation flux density for materials having a substantiallyrectangular hysteresis loop) to saturation flux density in the zerodirection. Such ux change will induce voltages in solenoids 23a and 24a,and in conductor 21a. The voltage induced in conductor 21a will appearon conductor 31a, and will be detected and accepted as yan *indicationof a stored one by data utilization device 104. The central part of theportion of tape 22h within solenoid 23a will be subjected to the samemagnetizing field as the central part of the corresponding portion oftape 22a; but since a zero sense or direction of remanent magnetizationalready exists in that portion of tape 22h, the only effect of thisapplied reading magnetizing field will be to produce the slight fluxchange corresponding to a transition from remanence to saturation, whichWill produce only a very slight disturbance potential on conductors 2lband 31h, and which will have no effect upon data utilization device 104,which will therefore operate on the basis that failure to receive atthis time a voltage on conductor 31b corresponds logically to receipt ofa zero signal. Thus the `data digits 1, 0, will have been read andutilized.

The tape portion having a zero sense of magnetization will be unchangedby the reading operation, but that tape portion whose extremes are in aone sense of magnetization will have Ia central part in a zero sense(cf. FIG. 2b), if the field from the extreme parts is not sufficient byitself to restore the central part to the one sense yat the cessation ofthe reading eld. For this reason, at some time before the next readingoperation (and preferably immediately after the cessation of the readingpulse) the read-restore current source 105 must draw from ground throughsolenoid 24a and conductor 34a a restoring pulse of conventional currentof such magnitude less than the magnitude of the reading pulse that theeld produced by its passage through solenoid 24a will suffice, with thefields from the extreme parts of the lefthand portion of tape 22a, torestore the central part of that tape portion to a one sense ofmagnetization (cf. FIG. 2a); but the restoring field thus produced willbe insuicient, against the opposing elds of the extreme parts of theleft-hand portion of tape 22h, to reverse the magnetization of thecentral part of that tape portion to the one sense (cf. FIG. 2c). Thusthe tape portions containing a magnetically stored one may be restored,to a complete one sense of magnetization without altering the zerosense of tape portions containing a magnetically stored zero Thus therehave been described the operations of clearing, writing or storing datain chosen parts of the store, reading from selected parts of theA store,and restoring, which are'all the functions necessary to be performed inthe use of the store. Particular attention is invited to the novel `factthat the reading and restoration operation may be repeated an unlimitednumber of times without the necessity of reference to any external storeor `register to permit the Iregeneration of data destroyed by thereading process; the reading operation here taught leaves magneticallystored in a part of the tape a record of what the stored data was beforethe reading operation; and the .restoration operation is performed, notto replace data which has been destroyed and lost from the store, but tomake it possible to read the information once more.

Since the physical operation of this invention depends more basicallyupon magnetizing fields (the term magnetizing being preferred for the`quantity symbolized as H to distinguish it from the quantity symbolizedas B which is sometimes called the magnetic field in a ferromagneticmaterial) than upon the particular means used t-o produce thosemagnetizing elds, it is apparent that ordinary skill in the art willsuggest a large number of alternate ways of practicing the principlesherein taught. Thus, in lthe writing operation described, it would bepossible to apply to solenoid 23a ya current sufiiciently greater thanthe permissive current here specified, to magnetize all tape portionsWithin the solenoid in the one sense, and to achieve selective writingby sending, from data source 182 via conductor 31h through conductor 11bto ground a pulse of conventional current of such .magnitude that thecircular magnetizing field which it will produce around conductor 11bwill inhibit the magnetization in the one sense of the portion of tape22h lying within solenoid 23a, but will be insuiiicient to alter themagnetization of portions of tape 2'2b lying outside the solenoid 23a.Similarly, it is possible to provide an additional solenoid whosemagnetizing field will extend the entire active length of the tape andconductor assemblies, and to pass through such a solenoid a continuouscurrent of such magnitude that it will provide the requisite restoringfield at all central parts of -all tape portions; or a similar effectmay be produced by passing a continuous current of appropriate directionand `magnitude through the solenoids 24a and 24h at all times exceptwhen the reading pulse is applied. Many obviously equivalentpermutations are available to apply my invention to particularsituations where its advantages are best enjoyed by some embodimentother than the one here represented.

As a practical point, the use of magnetic materials of suiciently lowcoercive force has been found to permit dispensing entirely with anyother lrestoring field except that produced on the central part of atape portion by the extreme portions; such material may be used in theconfiguration of FIGURE l with the simple alteration that read-restorecurrent source may logically be c-hanged to read-current source 105, andwill provide only `read pulses as described, but no restoring current.The non-linearity of the magnetic characteristics of the materialsinvolved and the somewhat complex geometry render it extremely dithcultto calculate mathematically the minimum ratio of total bit portionlength to central part length which will produce this self-restorationfor material of given maximum remanent flux density and coercive force.However, it is a general principle that, for a given geometry, thatratio will decrease as the ratio of maximum remanent flux density tocoercive force is increased. This increase, of course, must be achievedeit-her by the substitution of a different material, or by thealte-ration of the properties of the material by some physicaltreatment, since it is a physical characteristic of the material.Self-restoration has been elements, conductor 21a was a tungsten wire0.006 inch (six mils) in nominal diameter, plated to a nominal diameterof 0.00625 (six and one-fourth mils) with ironnickel alloy having apreferred direction of magnetization substantially helical about thelongitudinal axis of Y This platin-g was the equivalent of the The anglebet-Ween the prethe lwire 21a. ferromagnetic material 22a.

ferred direction of the ferromagnetic material and theV central orlongitudinal axis of the wire 21a was nominally between 76.2 and 79.8degrees, this range being calculated from the direction of the fieldexisting during the formation of the ferromagnetic material. Coil 24aconsisted of turns of insulated wire #36 A.W.G. (nominal diameter -fvemils) one thirty-second of an inch long. The length of solenoid :23a wasone inch; the spacing between adjacent ends of solenoids 23a and 23b wastwo-tenths inch. The coercive force of the magnetic materialtwasmeasured as 6.34 oersteds. Under these conditions, it was found that theapplication of 0.400 ampere to coil 24a caused the central portion ofthe magnetic material on conductor 21a, i.e., that part lyingsubstantially within vcoil 24a, to be switched in about 0.5microseconds, giving an output of 30 millivolts across the ends t ofconductor 2da; and -it was also found thatthis operation could berepeated an indefinite number of times without any intermediaterestoration operation. Such a test |is typical of the only feasiblemeans of establishing self-restoration, since the kswitching or iiuxchange can be detected only by observation of induced voltages.

While the combination of magnetic tape and conductor in accordance withthe teaching of Blades, hereinbefore referenced, is convenient forteaching my invention, in

that it permits the clarifying developments of FIGURES Y 2a, 2b, and 2c,equivalents in the functioning of my invention are the magneticconductor having a helical direction of easy ymagnetization produced bymechanical twisting, as taught by Bobeck of reference, and indeed anymeans providing one or more conductors through which current may bepassed to provide a magnetizin-g field component parallel to thedirection of easy magt netization of a ferromagnetic element which is ofsuch extent that .reading out may lbe accomplished by observing voltagesinduced by the reversal of flux in a partonly of such element, theremaining parts of such element retaining their informative sense ofmagnetization suiciently to insure that the reversed part may be-restored to a like'- sense of magnetization. may be a portion of alarger piece of ferromagnetic material. Thus, a central conductor ofnon-magnetic material plated or otherwise coated with a ferromagneticmaterial having a substantially rectangular hysteresis loop Such..element and having a direction of easy magnetization substant tiallyhelical about the axis of such a central conductor can be used directlyto replace the assembly of conductor 21a and tape 22a represented inFIGURE l.

The magnetizing fields produced by solenoids and by currents throughstraight conductors are subject to fairly f missirble tolerances in suchvalues must be calculated for the particular limits of coercive force tobe employed. As indicated in Bobeck of reference, the helicaldisposition of the magnetic flux around the central conductor producesmultiple interlinkage between the flux in the tape and the centralconductor, so that the voltages of the signals read out are of the orderof tens or even hundreds of fmillivolts, which may be amplified 'asdesired by known means without the noise and other difficulties whichattend the amplification of signalsofmuch lower amplitude.

General references pertaining to the computer and dataprocessingartywhich may be'useful1in considering some of the applications of myinvention are thev following: publicationsof the Institute of RadioEngineers, 1 East 79 Street, New York City, N. Y., especially thepublications of the Professional Group onrElectronic Computers;publications of the American Institute of Electrical Engineers,

33 West 39 Street, New'York City, N. Y., especially 'Y Communication andElectronics;publications of the Association for Computing Machinery, NewYork City, N.Y., and a general reference on the generation of-pulses ofVcontrolled shape and amplitude, -Waveforrns, 'volurne 19 of the M.I.T.Radiation Laboratory Series, published by the McGraw-Hill Book Company,of New York,

Toronto, and London."

What is claimed is:

1. A magnetic data store comprising a piece of magnetic material havinga substantially rectangular hysteresis characteristic; means formagnetizing a portion of saidmagnetic material in `a first directioncorresponding to a first value ofdata to be `stored and formagnetizingsaid portion of said material in a Vsecond `directionopposite.

to said rst direction to correspond to a second value of data to bestored; means for magnetizing a central part only of said.portion ofsaid 'magnetic :material in said first direction; electrical means fordetecting the .ux change accompanying the said magnetizing of saidcentral part of said portion of said magneticmaterial in said firstdirection; means for applying to said central part of said portion ofYsaid magnetic material a magnetizing field having a component -in saidsecond direction of magnitude` suilicient to magnetize said central partof said Vportion of said magnetic material in said second direction ifthe extreme or non-central parts of said portion of said magneticmaterial are magnetized in said second direction, but not suflicientI tomagnetize said central part vof said portion of said magnetic materialin said second direction if the extremeyor non-central parts of saidportion of said magnetic `material are magnetized in said rst direction.

2. A magnetic data store comprising magnetic material having a preferreddirection of magnetization along which said magnetic material exhibits asubstantially `rectangular hysteresis; loop, recording meansformagnetizing individual portions of said magnetic material in a rst sensealong said preferredtdirection to representa first value of informationand in a second sense to represent a second value of information,sampling means for magnetizing a med-ian part only of lasaidindividualportion .in said first sensedetecting means -for detectingthe magnitude of the change of magnetization produced by operation ofsaid sampling means, restoring means for Vapplying to said median partof said individual portion a magnetizing field in said second ,sense andof intensity sufli-cient to magnetize said median part of'saidindividual portion in said second sense if, and only if, the non-medianpartsof said individual portion are magnetized 'in said 'second.sense.

3. A magnetic data store comprising a central'conductor surrounded bymagnetic material having a direction of easy magnetization substantiallyhelical around said central conductor and exhibiting a substantiallyrectangular hysteresis characteristic, iirst solenoids of predeterminedlength wound externallyyaround said central conductorand Vsaid magneticmaterial at selected locations along the length ofsaid centralconductor, second solenoids of considerablyshorterilength than saidlirst solenoids, each of said secondA solenoidsbeingwound around thesaid central conductor and said magnetic material in a medialpositionzwith respect to the axial length of `a said rst solenoid.

4.- .A magnetic data store as claimed in claim 3, further ,i3characterized by the fact that ythe second solenoids claimed thereinhave a length not more than one fourth of the length of the firstsolenoids claimed therein.

5. In a magnetic data store in which one of two values of infor-mationis stored by magnetizing a volume of magnetic material having asubstantially rectangular magnetization characteristic in one of twopossible senses of remanent magnetization along a preferred direction ofmagnetization; means for magnetizing a part only of said volume of saidmagnetic material in a first said sense, means for applying in a secondsaid sense opposite to said first sense a magnetizing field componentsufiicient with the assistance of the magnetizing field produced by saidvolume exclusive of said part to magnetize said part in said secondsense, but insufficient in magnitude to magnetize said part in saidsecond sense when opposed by said magnetizing field of said volumeexclusive of said part.

6. A magnetic data store comprising 'a homogeneous magnetic element ofsubstantially uniform cross-sectional area, said magnetic element havinga substantially rectangular hysteresis characteristic along a preferreddirection of magnetization which is helical about said element, firstmeans for magnetizing at least a portion of said magnetic element in afirst sense of remanent magnetization to store a first value ofinformation and in a second sense of remanent magnetization to store asecond value of information, second means to apply to la part only ofsaid portion of said magnetic element a magnetizing field sufficient tomagnetize said part in said first sense, the length of said part being.a sufficiently small fraction of the length of s-aid portion that themagnetizing field produced by the Iremainder `of the said portion whenthe sense of magnetization of said remainder is opposite to the sense`of magnetization of said part will exceed at said part the coerciveforce of said part.

7. A magnetic data store comprising a magnetic element having adirection of preferred magnetization substanti-ally helical along whichsaid magnetic element exhibits a s-ubstantially rectangular hysteresischaracteristic, a first solenoid external to said magnetic elementhaving a central axis substantially parallel to the central helical axisof said magnetic element, and extending along at least a portion of thelength of said magnetic element; la second solenoid of considerablyshorter length than said first solenoid and being positioned external tosaid magnetic element, having a central axis substantially parallel tothe said central helical axis of said magnetic element, and extendingalong only a median part -of said portion of the axial length of saidmagnetic element.

8. A magnetic data store comprising a piece of magnetic material havinga substantially rectangular hysteresis characteristic; means formagnetizing various portions of said magnetic material in a firstdirection corresponding to a first value of various items of data to bestored, each said item corresponding to a said portion, and formagnetizing said various portions of said material in a second directionopposite to said first direction to correspond to a second value of saidvarious items of data to be stored; means for magnetizing a central partonly of selected said various portions of said magnetic material in saidfirst direction; electrical means for detecting the flux changesaccompanying the said magnetizing of said central parts of said selectedvarious portions of said magnetic material in said first direction;means for applying to said central par-t of each said selected portionof said magneti-c material a magnetizing field having a component insaid second direction -of magnitude sufficient to magnetize said centralpart of said selected portion of said magnetic material in said seconddirection if the extreme or non-central parts of said selected portionof said magnetic material are magnetized in said second direction, butnot sufficient to magnetize said central part of said selected portionof said magnetic material in said second direction if the extreme ornon-central parts of said selected portion of said magnetic material aremagnetized in said first direction.

9. A magnetic d-ata store comprising magnetic material having asubstantially rectangular hysteresis characteristic along a preferreddirection of magnetization which is s-ubstantially helical about thematerial, a first winding positioned externally around said magneticmaterial along at least a portion of the length thereof, recording meansincluding said first winding for magnetizing the said portion Iofmagnetic material in a first sense along said preferred direction torepresent a first value of information and in a second sense torepresent a second value of information, a second winding positionedexternally along -only a median part of the said portion of magneticmaterial encompassed by said first winding, sampling means includingsaid second Winding for magnetizing in said first sense only saidmedi-an part of the said portion of magnetic material, means fordetecting the magnitude of change of magnetization produced by operationof said sampling means, restoring means including said second windingfor applying only to said median part of said portion of magneticmaterial a magnetizing field in said second sense and of sufiicientintensity to magnetize said median part in said second sense if, andonly if, the nonmedian parts of the said portion of magnetic materialare magnetized in said second sense.

10. A magnetic data store comprising an electrical conductor coveredwith magnetic material capable of attaining opposed states of residualflux density in representing binary logical information, said magneticmaterial having a preferred direction of magnetization substantiallyhelical about said conductor, a first winding encompassing at least aportion of the magnetic material covering the length of said conductor,-recording means including said first Winding for magnetizing the saidportion of magnetic material in a first sense along said preferreddirection to represent a first value of information, and in a secondsense to represent a second value of information, a second Windi-ngencompassing only the median part of the said portion of magneticmaterial encompassed by said first winding, sampling means includingsaid second Winding for magnetizing in said first sense said median partonly 4of the said portion of magnetic material, the change inmagnetization produced by the operation of said sampling means inducinga voltage signal in said electrical cond-uctor, restoring meansincluding said second winding for applying to said median part only ofsaid portion of magnetic material a magnetizing field in said secondsense Iand of sufficient intensity to magnetize said median part in saidsecond sense if, and only if, the non-median parts of the said portionof magnetic material are magnetized in said second sense.

11. A magnetic data store comprising an electrical conductor havingwrapped therearound a strip of magnetic material capable of attainingopposed states of residual fiux density in representing binary logicalinformation, said magnetic material having a preferred direction ofmagnetization substantially helical about said conductor, a firstsolenoid encompassing at least a portion of the magnetic materialwrapped around the length of said conductor, means including said firstsolenoid for magnetizing the said portion of magnetic material to afirst state along said preferred direction to represent a first value ofinformation, and in a second state to represent a second value tofinformation, a second solenoid encompassing only the median part of thesaid portion of magnetic material encompassed by said first solenoid,circuit means including said second solenoid for magnetizing to saidfirst state said median part only of the said portion of magneticmaterial, the change in magnetization of said median part from one stateto its other state inducing a voltage signal in said electricalconductor, circuit means including -said second solenoid for applying tosaid median part only of said portion of magnetic material a magneticfield of sufficient intensity to magnetize said median parts of the saidportion of magnetic material are magnetized to said second state. t

12. A magnetic data store as defined in claim 11 further characterizedin that said second solenoid has a ylength not greater 'than ione-fourththe length of rst solenoid.

References Cited by the Examiner UNITED STATES PATENTS 16, FOREIGNPATENTS 7/ 1955 France..V

OTHERv REFERENCES Pages 822160 830,'Jlanuary 1954, Communications andElectronics.

Pages 95y to 98, January 19,58, Electrical Manufacturingjf vol. 61, No.1.

Pages 1319 to 1340, November 195 7,".The Bell System 10TechnicalJournal, 'vol. 36,'No. 6.

2,430,457 11/ 1947 Dimond 307-88 2,722,603 11/ 1955 Dmond 340-174BERNARD KONICK, Primary Exlmz'iner.'V

2,781,503 2/1957 Saunders 340-174 y 2,920,317 1/1960 Mauery 340 172WALTER W- BURNS, JR, IRVING L. SRGOW, 2,945,217 7/1960 Fisher et a1.340-174 15 Y x"?fs 2,984,825 5/ 1961 Fuller et al. 340-174 R. R.HUBBARD, I. W. MOFFITT, Assistant Examiners.

3. A MAGNETIC DATA STORE COMPRISING A CENTRAL CONDUCTOR SURROUNDED BYMAGNETIC MATERIAL HAVING A DIRECTION OF EASY MAGNETIZATION SUBSTANTIALLYHELICAL AROUND SAID CENTRAL CONDUCTOR AND EXHIBITING A SUBSTANTIALLYRECTANGULAR HYSTERESIS CHARACTERISTIC, FIRST SOLENOIDS OF PREDETERMINEDLENGTH WOUND EXTERNALLY AROUND SAID CENTRAL CONDUCTOR AND SAID MAGNETICMATERIAL AT SELECTED LOCATIONS ALONG THE LENGTH OF SAID CENTRALCONDUCTOR, SECOND SOLENOIDS OF CONSIDERABLY SHORTER LENGTH THAN SAIDFIRST SOLENOIDS, EACH OF SAID SECOND SOLENOIDS BEING WOUND AROUND THESAID CENTRAL CONDUCTOR AND SAID MAGNETIC MATERIAL IN A MEDIAL POSITIONWITH RESPECT TO THE AXIAL LENGTH OF A SAID FIRST SOLENOID.